Programmed cell death in the pancreas of Bufo bufo during metamorphosis

Abstract

Programmed cell death or apoptosis occurred in anuran amphibian larval pancreas as a remodelling agent, and was responsible for the reduction of the gland volume during metamorphosis. Apoptotic cells were recognisable by their morphological characteristics and could be immunocytochemically detected by means of the TUNEL reaction, which evidenced nuclear DNA fragmentation. During the last stages of prometamorphosis, that is in the period of hindlimb differentiation, only a few TUNEL positive cells occurred, whereas they increased at the beginning of metamorphic climax, that is at forelimb emergence and during tail regression. Under the electron microscope, the typical morphological characteristics of apoptosis were observed : decrease in size, and the presence of wide intercellular spaces and nuclei with dense chromatin masses arranged in crescents. The fragmentation of these cells produced the so-called 'apoptotic bodies ' : portions of cytoplasm lined by a membrane, containing nuclear fragments and cytoplasmic organites. Dead cell elimination is hypothesised to occur by phagocytic ingestion.

Apoptosis in amphibian organs during metamorphosis

“…This degeneration of pancreas is caused in part by apoptosis of cells around the blood vessels and pancreatic ducts. The number of apoptotic cells reaches a peak at Rossi's stage XIII (around NF stage 58-62), when forelimbs emerge [50]. …”

Xenopus pancreas development

“…The shrinkage of the pancreas that occurs at climax brings the various endocrine cells closer together (Maake et al, 1998). In addition, a “maturation” of the pancreatic system has been proposed to occur at climax (Maake et al, 1998; Accordi and Chimenti, 2001), which involves limited cell death and changes in insulin expression. In the tadpole, β cells are present in small clusters (Kelly and Melton, 2000), but during the eight days of metamorphic climax, while the exocrine pancreas dedifferentiates, these clusters are induced by TH to become larger (Fig.…”

Morphology of the pancreas of some species belonging to the genera Phelsuma and Gecko (family Gekkonidae): evidence of apoptotic process during the seasonal cycle

“…There are no available data in literature yet concerning apoptotic events in the pancreas of reptiles, while they occurred, as remodeling agents, in the pancreas of the anuran amphibian larvae, in which they were also responsible for the reduction of gland volume during metamorphosis (Accordi and Chimenti 2001), and in Xenopus small intestine during metamorphosis (Ishizuya-Oka and Ueda 1996). Apoptotic events have been described in the small intestine of adult Burmese python (Starck and Beese 2001), with the number of apoptotic cells rapidly increasing after feeding; this is a highly unexpected result, because, instead, in mice and rats, starvation is the event that induces apoptosis in the gut mucosa and the liver (Tessitore et al 1999;Iwakiri et al 2001;Chappel et al 2003).…”